Can an Application Ignore PCIe flow Control Credits?

Hi corestar,

My apologies on the delayed response.

Yes, the flow control signal (tx_cred_*) can be ignored and honoring tx_st_ready is sufficient. The Hard IP performs the mandatory PCIe credit check on every TLP internally; if credits are short it blocks the TLP (and all following ones) and expresses that back-pressure solely by deasserting tx_st_ready. The flow control signals are needed to track credits to optimize the throughput, which is optional. 

Regarding the credit limits, the Avalon-ST TX datapath does expose them. The six credit limit signals tx_cred_hdrfcp/datafcp, tx_cred_hdrfcnp/datafcnp, tx_cred_hdrfccp/datafccp carry the current per-type credit limits; the tx_cred_fchipcons strobes each credit the Hard IP consumes; and tx_cred_fc_infinite flags infinite types.

Thanks. 

Best Regards, 

Ven